The present application relates generally to controls for dual-fuel engines and more particularly, but not exclusively to dual-fuel engine combustion mode transition controls. Dual-fuel engines hold the promise of a number of potential economic and environmental benefits through the combustion of different ratios or proportions of two or more types of fuels during different modes of operation. A number of proposals have been made for controlling dual-fuel engines in multiple operating modes including controlling transitions between operating modes. Certain proposals seek to maintain total fuel energy constant during a transition from one fueling mode to another. Such proposals suffer from a number of drawbacks, for example, gas lambda may fall outside of a desired range for a selected gaseous fuel quantity and since airflow control devices are incapable of adjusting airflow to the cylinders rapidly enough to obtain a desired lambda for a selected quantity of fuel. As a result, the engine may exhibit power surges and droops even if total fuel energy content remains constant. Other proposals seek to overcome these drawbacks by accounting for other engine operating parameters, for example, primary fuel excess air ratio sometimes referred to as lambda. Yet such proposals fail to account for multiple factors impacting combustion. Variations in fuel composition and energy content may add significant error to controls based upon fuel energy content and/or lambda. For example, when natural gas is utilized as a fuel source, variation in both energy content and fuel density may be encountered due to variation in the relative amount of methane and propane present in the fuel. Variation in the Cetane rating of diesel fuel may also occur. Variations in oxygen concentration due to changes in altitude may also introduce error. Variation in charge air density due to temperature and humidity variations presents a further source of error. Existing control proposals fail to account for or effectively accommodate such variability. Furthermore, existing control techniques including total fuel energy content controls and/or lambda control fail to adequately account for and mitigate post-cylinder engine emissions including, for example, hydrocarbon slip, engine NOx out, and other engine emissions. There remains a significant need for the unique controls methods, systems, and apparatuses disclosed herein.